Quick Answer. Neo-Malthusian theory holds that population growth is exponential and that human population growth can easily outstrip its food resources if not held in check with artificial birth control measures. It differs from traditional Malthusian theory in the proposed birth control solution.
Terrace farming is when farming is done on manmade terraces that have been built into slopes. When humans transform a slope into a series of flat surfaces, they form terraces. Crops are then grown on these flat surfaces rather than on the slope, preventing crops from sliding down the slope over time. The image below is of rice paddies grown on terraces. By building these terraces, water flows down and accumulates in each terrace. If the terraces did not exist, rainfall and water would flow from higher elevations down the hill/mountain, carrying important soil and nutrients with it. Building terraces prevents this from happening.
Cover crops are used occasionally in no-till farming to help control weeds and increase nutrients in the soil (by using legumes) or by using plants with long roots to pull mobile nutrients back up to the surface from lower layers of the soil.